Production of lithium compounds directly from lithium containing brines

ABSTRACT

A continuous process for directly preparing high purity lithium carbonate from lithium containing brines by preparing a brine containing about 6.0 wt % lithium and further containing other ions naturally occurring in brines; adding mother liquor containing carbonate to precipitate magnesium; adding a solution of CaO and sodium carbonate to remove calcium and any residual magnesium; precipitating lithium carbonate from the purified brine by adding soda ash solution; filtering to obtain solid lithium carbonate; preparing an aqueous slurry of the lithium carbonate and introducing carbon dioxide gas at a temperature from at least minus 10 to +40° C.; passing the lithium bicarbonate solution through a filter to clarify the solution; introducing said filtered lithium bicarbonate solution into a reactor and adjusting the temperature of the solution to from 60–100° C. to precipitate ultra-pure lithium carbonate.

This application is a continuation-in-part of U.S. Ser. No. 09/707,427,filed Nov. 7, 2000, now U. S. Pat. No. 6,936,229 issued Aug. 30, 2005,which is a divisional application of U.S. Ser. No. 09/353,185 filed Jul.14, 1999, now U.S. Pat. No. 6,207,126, issued Mar. 27, 2001.

This application claims priority under 35 U.S.C. §119(e) from U.S.Provisional Application Nos. 60/100,340 filed Sep. 14, 1998 and60/093,024 filed Jul. 16, 1998.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to an integral process that uses a minimumnumber of process steps for producing chemical and high purity grades oflithium carbonate and lithium chloride directly from the same naturalbrine source. More generally, the method also relates to a method ofproducing purified metal carbonate salts that are generally insoluble inwater but which have corresponding bicarbonate salts that are more then75% soluble in water by reaction with carbon dioxide.

It is desirable, from a commercial standpoint, to provide a source oflithium low in sodium content because sodium becomes reactive andpotentially explosive in certain chemical processes, particularly thosein production of lithium metal from lithium salts. A substantial portionof presently available lithium is recovered from brines, which alsocontain high levels of sodium, making the production of low sodiumlithium salts difficult and expensive. At the present time, there doesnot exist a viable low cost integral processes for producing low sodiumlithium carbonate and chemical and high purity grades of lithiumchloride directly from natural brines containing lithium.

Natural brines that contain lithium also contain many constituents asillustrated in the following Table:

TABLE 1 NATURAL BRINE COMPOSITION Great Bonne- Salton Silver Dead Saltville Sea Peak Salar de Atacama Sea Lake Brine Brine Brine Brines OceanIsrael Utah Utah Calif Nevada Chile Na 1.05 3.0 7.0 9.4 5.71 6.2 7.175.70 K 0.038 0.6 0.4 0.6 1.42 0.8 1.85 1.71 Mg 0.123 4.0 0.8 0.4 0.0280.02 0.96 1.37 Li 0.0001 0.002 0.006 0.007 0.022 0.02 0.15 0.193 Ca 0.040.05 1.5 0.5 0.0 0.71 1.46 0.043 Cl 1.9 16.0 14.0 16.0 15.06 10.06 16.0417.07 Br 0.0065 0.4 0.0 0.0 0.0 0.002 0.005 0.005 B 0.0004 0.003 0.0070.007 0.039 0.005 0.04 0.04 Li/Mg 0.0008 0.0005 0.0075 0.0175 0.786 1.00.156 0.141 Li/K 0.0026 0.0033 0.015 0.0049 0.0155 0.016 0.081 0.113Li/Ca 0.0025 0.0064 0.2 0.0583 0.0008 1.0 4.84 0.244 Li/B 0.25 0.66660.857 1.0 0.051 4.0 3.75 4.83 (All values in weight percent)

Production of lithium carbonate and lithium chloride with acceptablequalities from such brines requires employing techniques to removespecific cations and anions that accompany the lithium in solution, andthen concentrating the lithium for extraction.

Individual applications require that these ion impurities be reduced tospecific maximum levels and a number of processes have been describedfor removing these impurities. For example, U.S. Pat. No. 5,219,550 toBrown and Boryta describes a method for producing chemical grade lithiumcarbonate from natural lithium containing brine by first removing mostof the components from the brine by concentrating utilizing solarevaporation techniques. Concentrating the brine with respect to lithiumby solar evaporation causes most of the unwanted components toprecipitate from the brine, i.e., salt out. Boron, which concentrateswith the lithium, is subsequently removed using an extraction process.The remaining magnesium is removed by adding a base to precipitatemagnesium carbonate and/or magnesium hydroxide, and the lithium isfinally precipitated from the purified brine as lithium carbonate by theaddition of soda ash. Other processes related to the above process aredisclosed in U.S. Pat. Nos. 4,036,718; 4,243,392; and 4,261,960.

Other techniques for producing purified lithium salts are known. Forexample, German Patent DE 19,541,558 to Wusson et al describes a processto reduce sodium from lithium chloride solutions by cooling. U.S. Pat.No. 4,859,343 to Kullberg et al describes an ion exchange method forremoving sodium from brines. U.S. Pat. No. 5,599,516 and Russian PatentNo. 9,419,280 describe absorption/ion exchange processes for recoveringlithium from brine.

U.S. Pat. No. 4,980,136 discloses a procedure for preparing chemicalgrade and low sodium lithium chloride (battery grade, less than 20 ppmsodium and less than 5 ppm magnesium) from concentrated natural brine bycrystallizing lithium chloride from a magnesium/lithium chloride brineto produce a chemical grade of lithium chloride crystal. This isfollowed by alcoholic extraction of the soluble lithium chloride fromthe crystal leaving sodium chloride as the insoluble phase. The alcoholsolution containing the lithium chloride is then filtered and evaporatedto form a high purity grade of lithium chloride crystal.

East German Patent DD 257,245 describes a method for recovering lithiumchloride from concentrated brine containing both calcium chloride andmagnesium chloride and selectively extracting lithium chloride withalcohol. Other patents related to such processes include U.S. Pat. Nos.4,271,131 and 4,274,834.

U.S. Pat. No. 4,207,297 describes production of a low sodium lithiumcarbonate (sodium less than 10 ppm in lithium carbonate) from technicallithium carbonate. This is accomplished by reacting lithium carbonatewith lime followed by filtration to produce a lithium hydroxidesolution. The solution is subsequently purified with just enough carbondioxide to remove the residual calcium and filtered. More carbon dioxidegas is added to the purified lithium hydroxide solution tore-precipitate lithium carbonate crystal as a high purity product.

Except for the methods described in DE 19,541,558, U.S. Pat. Nos.4,243,392 and 5,219,550, the methods of the prior art are not practicedtoday because they are either technically or economically not viable.

Another process for producing lithium chloride is set forth in ChileanPatent Application No. 550-95, which describes a procedure whereby apurified brine containing essentially lithium chloride is directlyproduced from natural brines that have been concentrated by solarevaporation and treated by an extraction process to remove boron.However, the sodium, calcium, and sulfate levels in the resultant brineare too high to be an acceptable brine source of lithium chloride forproducing a technical grade lithium metal, primarily because the twomajor remaining impurities, sodium and magnesium, have to be furtherreduced to acceptable levels to produce chemical grade lithium chloridecrystal. Specifically, magnesium must be reduced to less than 0.005 wt %Mg, and sodium to less than 0.16 wt % Na in the anhydrous lithiumchloride salt. Salting out anhydrous lithium chloride directly frombrine above 110° C. in a vacuum crystallizer as described in U.S. Pat.No. 4,980,136 yields a lithium chloride containing at best 0.07 wt % Mgand 0.17 wt % Na.

It is accepted, although not proven, that lithium chloride crystalcontaining 0.07 wt % Mg may be too high in magnesium to be used forproducing lithium metal and for subsequent use in the production oflithium organometallic compounds. Thus, the industry demands thatorganolithium catalysts in polymerization reactions be low in magnesium.Lithium chloride high in magnesium can also adversely affect theoperation of the lithium electrolysis cell when producing the lithiummetal.

As noted above, the sodium impurity in the lithium chloride crystalreports directly to the metal when producing lithium metal. Thus, lowsodium lithium salts are desirable. Sodium in lithium chloride crystalabove 0.6 wt % produces metal containing 1 wt % sodium or higher. Sodiumconcentrations of about 1 wt % in lithium metal or above render thelithium metal more reactive to natural components of air. This makes themetal more difficult and more dangerous to handle. Table 2 sets forthdata concerning sodium limits and tolerances in different lithiumsources:

TABLE 2 SODIUM CONTENT OF LITHIUM CHLORIDE Maximum Na in LiCl Brown &limits for chloride required Becherman chemical grade for battery gradechemical grade metal metal % Lithium chloride 99.2 99.2 99.8 % Na** 0.170.04 0.0006 **wt % in Lithium chloride

Commercial methods employed to produce low sodium lithium carbonate andlithium chloride on a commercial scale include extraction of lithiumcompounds from mineral deposits such as spodumene bearing ore andnatural brines. A number of processes have been described and some havebeen commercialized for producing lithium carbonate from these sources.

One such commercial method involves extraction of lithium from a lithiumcontaining ore or brine to make a pure lithium sulfate solution such asdescribed in U.S. Pat. No. 2,516,109, or a lithium chloride solutionsuch as described in U.S. Pat. No. 5,219,550. After purifying thesolutions, sodium carbonate is added as either a solid or a solution toprecipitate lithium carbonate crystals. The lithium carbonate issubsequently filtered from the spent liquor (mother liquor), and thelithium carbonate is washed, dried, and packaged.

Lithium carbonate is often used as a feed material for producing otherlithium compounds such as lithium chloride, lithium hydroxidemonohydrate, lithium bromide, lithium nitrate, lithium sulfate, lithiumniobate, etc. Lithium carbonate itself is used as an additive in theelectrolytic production of aluminum to improve cell efficiency and as asource of lithium oxide in the making of glass, enamels, and ceramics.High purity lithium carbonate is used in medical applications.

For example, a presently used commercial procedure for producingchemical grade lithium chloride is to react a lithium base such aslithium carbonate or lithium hydroxide monohydrate with concentratedhydrochloric acid to produce a pure lithium chloride brine. Theresultant lithium chloride brine is evaporated in a vacuum crystallizerat or above 110° C. to produce an anhydrous lithium chloride crystalproduct. This procedure yields a product that meets most commercialspecifications for chemical grade lithium chloride, but not low sodiumgrades of lithium chloride. Chemical grade lithium chloride is suitablefor air drying applications, fluxes, an intermediate in manufacture ofmixed ion-exchange zeolites, and as a feed to an electrolysis cell forproducing chemical grade lithium metal. Chemical grade lithium metal isused, inter alia, to produce lithium organometallic compounds. Thesecompounds are used as a catalyst in the polymerization andpharmaceutical industry.

Chemical grade anhydrous lithium chloride should contain less than 0.16%sodium in order to produce metal containing less than 1% sodium. Theimportance of minimizing the sodium content in the metal and the costsassociated therewith are the principle reasons for using lithiumhydroxide monohydrate or lithium carbonate as the raw material forproducing lithium chloride and, subsequently, lithium metal. Inconsideration, low sodium lithium chloride, typically contains less than0.0008 wt % sodium, and is commercially produced to manufacture lowsodium lithium metal suitable for battery applications and for producingalloys.

Commercially, low sodium lithium chloride is produced indirectly fromchemical grade lithium carbonate. Chemical grade lithium carbonate isproduced from Silver Peak Nev. brine, Salar de Atacama brines in Chile,Hombre Muerto brines in Argentina, and from spodumene ore (mined inNorth Carolina). The lithium carbonate is converted to lithium hydroxidemonohydrate by reaction with slaked lime. The resultant slurry containsprecipitated calcium carbonate and a 2–4 wt % lithium hydroxidesolution, which are separated by filtration.

The lithium hydroxide solution is concentrated in a vacuum evaporationcrystallizer in which the lithium hydroxide monohydrate is crystallized,leaving the soluble sodium in the mother liquor solution. The crystallithium hydroxide monohydrate is separated from the mother liquor anddried. This salt normally contains between 0.02 and 0.04% sodium. Tofurther reduce the sodium levels, the lithium hydroxide monohydrate mustbe dissolved in pure water and recrystallized, and subsequently reactedwith pure hydrochloric acid to form a concentrated lithium chloridebrine containing less than 10 ppm sodium. The resultant lithium chloridesolution is then evaporated to dryness to yield anhydrous lithiumchloride suitable for producing battery grade lithium metal containingless than 100 ppm sodium. The above process requires seven majorprocessing steps described as follows:

1) Extraction and purification of a low boron aqueous solutioncontaining 0.66 to 6 wt % Li from lithium containing ore or naturalbrine;

2) Purification of the brine with respect to magnesium and calcium andfiltered;

3) Precipitation of lithium carbonate from the purified brine byaddition of Na₂CO₃, and filtering and drying the lithium carbonate;

4) Reacting slaked lime and lithium carbonate to produce a LiOH solutionand filtering;

5) Crystallizing LiOH·H₂O in a vacuum crystallizer;

6) Dissolving the LiOH·H₂O crystals and re-crystallizing LiOH·H₂O fromsolution; and

7) Reacting high purity HCl with re-crystallized LiOH·H₂O to produce ahigh purity lithium chloride brine from which low sodium lithiumchloride is crystallized and drying the lithium chloride.

Low sodium lithium carbonate can be prepared from re-crystallizedLiOH·H₂O using the first part of the process described above. Therecrystallized LiOH·H₂O is then mixed with water and reacted with CO₂ toprecipitate the lithium carbonate. The processing steps are set forthbelow:

1) Extraction and purification of a low boron aqueous solutioncontaining 0.66 to 6 wt % Li from lithium containing ore or naturalbrine;

2) Purifying the brine is then purified with respect to magnesium andcalcium and filtered.

3) Precipitate Li₂CO₃ from the purified brine with the addition ofNa₂CO₃, filtered and dried.

4) React slaked lime and Li₂CO₃ to produce a LiOH solution and filter.

5) LiOH·H₂O is crystallized in a vacuum crystallizer.

6) Dissolve again and re-crystallize LiOH·H₂O from solution.

7) React CO₂ gas with a slurry containing re-crystallized LiOH·H₂O toCrystallize low sodium high purity lithium carbonate crystal, filter anddry.

Production of lithium chloride direct from concentrated brine has alsobeen described in U.S. Pat. No. 4,274,834.

The present invention provides an integral and novel process whichreduces the number of major processing steps for producing chemical(technical) grade and low sodium lithium carbonate and lithium chloridedirectly from natural lithium containing brines concentrated to about6.0 wt % Li without the lithium hydroxide monohydrate single and doublerecrystallization steps present in the processes of the prior art.

The present invention also relates to a method for preparing chemicalgrade lithium chloride direct from the same concentrated starting brineas that used to prepare the lithium carbonate.

The present invention incorporates the process described in U.S. Pat.No. 5,219,550 to produce a chemical grade lithium carbonate tospecifically utilize the mother liquor by-product stream from thatprocess to recover lithium from the magnesium containing purificationmuds that are formed when producing lithium chloride directly frombrine, eliminating the steps of first precipitating lithium carbonate orlithium hydroxide and then transforming these salts to lithium chloride.Additionally, the process of the invention yields a high purity lithiumcarbonate having less than about 0.002 wt % sodium using a carbondioxide/bicarbonate cycle, and a process of preparing a high puritylithium chloride by reacting the high purity lithium carbonate with ahigh purity hydrochloric acid.

A preferred method is directed to a continuous process for directlypreparing high purity lithium carbonate from lithium containing brinesby preparing a brine containing about 6.0 wt % lithium and furthercontaining other ions such as sodium, magnesium, calcium, and sulfatesnaturally occurring in brines; adding mother liquor containing carbonatefrom a prior precipitation step to precipitate magnesium as magnesiumcarbonate; adding a solution of CaO and sodium carbonate to removecalcium and residual magnesium; precipitating lithium carbonate from thepurified brine by adding soda ash solution; filtering the resultantsolution to obtain solid lithium carbonate; preparing an aqueous slurryof the lithium carbonate in a reactor equipped with an inlet forintroducing carbon dioxide gas into said aqueous slurry to form anaqueous lithium bicarbonate solution, the reactor being at a temperaturefrom at least minus 10 to +40° C.; passing said aqueous lithiumbicarbonate solution through a filter to clarify the solution andoptionally an ion exchange column for further calcium and magnesiumremoval; introducing said filtered lithium bicarbonate solution into asecond reactor and adjusting of the solution to from 60–100° C. toprecipitate ultra-pure lithium carbonate with sodium less than 0.0002 wt%, calcium less than 0.00007 wt % and magnesium less than 0.00001 wt %.

Another preferred embodiment relates to a continuous process fordirectly preparing high purity lithium carbonate from lithium containingbrines by preparing a brine containing about 6.0 wt % lithium andfurther containing other ions such as sodium, magnesium, calcium, andsulfates naturally occurring in brines; adding CaO to remove magnesium;adding mother liquor containing carbonate from a prior precipitationstep and soda ash solution to precipitate calcium carbonate; filteringto remove calcium carbonate and to yield a purified lithium containingbrine; adding soda ash to said purified brine to precipitate lithiumcarbonate; filtering the solution to recover the precipitated lithiumcarbonate, preparing an aqueous lithium carbonate slurry in a reactorwhere such reactor is equipped with an inlet for introducing carbondioxide gas into the lithium carbonate slurry to produce an aqueouslithium bicarbonate solution, wherein the reactor is at a temperaturefrom at least minus 10 to +40° C.; passing the aqueous lithiumbicarbonate solution through a clarifying filter and optionally an ionexchange column for further calcium and magnesium removal; introducingthe filtered solution into a second reactor and adjusting thetemperature of the solution to from 60–100° C. to precipitate theultra-pure lithium carbonate with sodium less than 0.0002 wt %, calciumless than 0.00007 wt % and magnesium less than 0.00001 wt %.

In preferred embodiment, the lithium bicarbonate is only passed througha filter and proceeding to the second reactor at 60–100° C. toprecipitate low sodium lithium carbonate with a sodium content of lessthan 0.0002 wt %.

In other preferred embodiments the lithium bicarbonate is only passedthrough a filter and proceeding to the second reactor at 60–100° C. toprecipitate low sodium lithium carbonate with a sodium content of lessthan 0.0002 wt %.

In other embodiments, the carbon dioxide absorption reactor is fromminus 10° C. but not more than 40° C., and preferably from 0–35° C., andthe temperature of the reactor for precipitating high purity lithiumcarbonate is from 60–100° C., preferably 70–95° C.

A preferred ion exchange column contains Amberlite IRC-718 as a cationexchange resin.

The methods are conducted at less than or equal to atmospheric pressure.

The high purity lithium carbonate preferably contains less than 20 ppmsodium as an impurity, preferably less than 2 ppm sodium.

In a preferred embodiment, the purified lithium carbonate contains

High Purity Low Sodium Wt % Li₂CO₃ Li2CO3 >99.4 Mg <0.0007 Na <0.0010 K<0.00025 Ca <0.0120 B <0.0001 Al <0.0002 As <0.0001 Fe <0.0001 Si<0.0010 Zn <0.00005 SO4 <0.037 Cl <0.005

In another preferred embodiment, the purified lithium carbonate has thefollowing composition:

Ultra-High Purity Wt % Li2CO3 Li2CO3 >99.995 Mg <0.00001 Na <0.0002 K<0.00015 Ca <0.00007 B <0.0001 Al <0.0002 As <0.0001 Fe <0.0001 Si<0.00011 Zn <0.000014 SO4 <0.0030 Cl <0.005

The invention also relates to high purity lithium chloride containingless than 20 ppm sodium, and preferably less than 8 ppm sodium.

Such high purity lithium chloride is prepared by a process which is alsoa part of the present invention, the process including the steps ofreacting lithium carbonate having a sodium content of less than 0.0002wt % with hydrochloric acid having less than 1 ppm sodium to producehigh purity lithium chloride having sodium content of less than 0.001 wt%. The lithium carbonate may be prepared according to processesdescribed above and elsewhere herein.

The present invention also provides an apparatus for continuouslypurifying lithium carbonate having a dissolver which is a baffledreactor to dissolve lithium carbonate that includes a mixer/disperser, acarbon dioxide gas dispersion tube, a wash water filtrate/mother liquorfiltrate recycle line, a cooler, a stilling well to separate gas andundissolved lithium carbonate solids from the resultant lithiumbicarbonate solution, and a continuous chemical grade lithium carbonatecrystal feeder; an inline filter to remove insoluble impurities from thelithium bicarbonate solution coming from the stilling well; a heatexchanger to recover heat from the hot mother liquor that is recycled tothe dissolver; a heated gas sealed crystallizer with mixer to decomposethe lithium bicarbonate solution to form low sodium lithium carbonatecrystals, carbon dioxide gas, and mother liquor; a slurry valve toremove the low sodium lithium carbonate crystals and mother liquor fromthe gas sealed crystallizer; a gas line to continuously return thecarbon dioxide produced in the crystallizer to the dissolver; aseparator such as a continuous belt filter to separate the low sodiumlithium carbonate from the mother liquor and a wash water section towash the lithium carbonate crystals; a pump and line to return themother liquor and wash filtrate to the dissolver; a mother liquor bleedto control the sodium level and to maintain a constant liquid volume;and a carbon dioxide source. Preferably, the apparatus has a reactorusing absorption columns, such as a sieve tray or a Scheibel column, tofacilitate absorption of carbon dioxide in the aqueous slurries.

The invention also relates to a method for purifying metal carbonatesthat are insoluble in water but have corresponding metal bicarbonatesalts that are more than 75% by wt. soluble in water by preparing anaqueous slurry of said metal carbonate; introducing carbon dioxide gasinto said aqueous slurry to form a corresponding metal bicarbonatesolution; and heating the metal bicarbonate solution to form a purifiedmetal carbonate, wherein the heating is such that the temperature of thesolution is raised to a temperature at which the metal carbonate isinsoluble to precipitate the purified metal carbonate. Lithium is apreferred metal.

The pressures used to make any of these salts according to the processesmay be, e.g., less than or equal to atmospheric pressure.

A preferred cation exchange resin is Amberlite IRC-718 commerciallyavailable from Rohm and Haas.

The purified salts prepared according to the methods of the inventionalso preferably, have a potassium content of less than 20 ppm, a calciumcontent of not greater than 140 ppm Ca, a magnesium content of from 3–7ppm, and not greater than 400 ppm sulfate (SO₄ ⁻), or any combination ofthese.

Any patents and references cited herein are incorporated by reference intheir entireties.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flow diagram showing the production of technical gradelithium carbonate according to the present invention;

FIG. 2 is a flow diagram showing the production of low sodium lithiumcarbonate according to the present invention;

FIG. 3 is a flow diagram of the process of direct lithium chloriderecovery from brine according to the present invention of a preferredembodiment of the invention;

FIG. 4 is a laboratory apparatus for producing low sodium lithiumcarbonate according to the present invention;

FIG. 5 is an apparatus with an absorption column for preparing the lowsodium lithium carbonate according to the present invention whereincarbon dioxide from the process reaction is recycled into the absorptioncolumn;

FIG. 6 shows a preferred apparatus having a sieve column for preparingthe low sodium lithium carbonate of the present invention; and

FIG. 7 shows an alternative apparatus having a Scheibel column forpreparing the low sodium lithium carbonate of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following describes in detail the process for making low sodiumlithium carbonate from chemical grade lithium carbonate without the needfor using the double crystallization process for making high puritylithium hydroxide monohydrate.

There are different chemical compositions of brine that exists in naturethat contain lithium (see Table 1, supra). For example, there exist inthe Salar de Atacama basin two different types of lithium containingbrine. These are described as high sulfate brine and high calcium brine.Sulfate may be removed from the brine by adding either lime or a calciumchloride by-product from another source, or mixing with a brinecontaining calcium to precipitate the calcium and sulfate as gypsum(CaSO₄.2H₂O). This produces a low calcium low sulfate brine that can besolar concentrated and have a higher lithium yield than concentrating abrine containing sulfate or calcium. Reducing the sulfate in the brinealso allows for better recoveries of potash from brines that naturallycontain potassium.

The natural brine is concentrated to a lithium content of about 6.0%,e.g. 6.0–6.5% by solar evaporation. During the solar evaporationprocess, gypsum continues to co-precipitate with sodium chloride whensulfate and calcium are stoichiometrically balanced. With continuedevaporation, potassium chloride and sodium chloride precipitate untilthe lithium and magnesium concentrations increases to about 0.76 wt % Liand 5.2 wt % Mg. Concentrating the brine from 0.76 wt % Li to 1.4 wt %Li will precipitate the carnallite salt (KCl·MgCl₂.6H₂O). This reducesthe Mg:Li ratio in solution from about 6.8:1 to 5.1:1, and removes mostof the sodium and potassium from solution. Continued evaporation andconcentration of the brine from 1.4 wt % Li to 4.2 wt % Li precipitatesthe bischofite salt (MgCl₂.6H₂O). This further reduces the Mg:Li ratioto 0.93:1.

Further concentration of the brine from about 4.2 wt % Li to about 6.2wt % Li precipitates the lithium camallite salt (LiCl·MgCl₂.7H₂O). Thisfurther reduces the Mg:Li ratio to about 0.24:1.

To improve the lithium yield when concentrating the brine to about 6 wt% lithium, the lithium precipitated from brine as lithium carnallite isconverted to the bischofite salt and lithium chloride brine by mixingthe lithium camallite salt with brine containing between 1.4 to 3 wt %Li. In order to convert 100% of lithium carnallite to bischofite, theresultant recovered brine contained in the bischofite salt ponds mustnot exceed a lithium concentration of 4.2 wt % Li.

Magnesium polyborates precipitate slowly from the concentrated brines.This usually causes the boron salts to super saturate when the brineresident time in the ponds is short. As a result, the boron content ofthe brines can range between 0.5 to 1.2 wt % boron.

At ambient conditions, the concentrated brine will contain on theaverage:

6.0 ± 0.3 % Li 1.65 ± 0.4  % Mg 0.08 % Na 0.02 % K 0.033 % Ca 0.019 %SO₄ 0.8 ± 0.2 % B  35 ± 0.5 % Cl

Natural brines containing lithium, magnesium, potassium, sodium, boron,wherein calcium and sulfate are stoichiometrically balanced, will havethis general composition when evaporated and concentrated under ambientconditions by solar evaporation to 6 wt % lithium. Brine containing 6.5wt % Li cannot be further concentrated because, at ambient conditions,this concentration defines the “end point” or the drying up point of theLi—Mg—Cl—H₂O system. Further evaporation will not change composition ofthe brine or the Mg:Li ratio of the brine, and will serve only toprecipitate a mixture of lithium carnallite and lithium chloridemonohydrate (LiCl·H₂O) as the brine evaporates. The resultant saltmixture will have the same Mg:Li ratio as the end point brine.

The boron and magnesium remaining in brine concentrated to about 6 wt %Li must be removed in order to make a suitable lithium carbonateproduct. It is preferred that boron is removed by an alcohol extractionsuch as described in U.S. Pat. No. 5,219,550, hereby incorporated byreference in its entirety. This extraction process reduces the boron inthe concentrated brine to less than about 0.0005 wt % B.

Procedures known in the art for directly removing magnesium fromconcentrated brine as magnesium hydroxide are costly because valuablelithium will be retained by the magnesium hydroxide which forms as avoluminous precipitate which is difficult to filter. To achieve maximumlithium yields and facilitate filtration, the magnesium may be removedin two steps. As much as 97% of the magnesium may be removed asmagnesium carbonate (MgCO₃) by mixing the concentrated brine withrecycled mother liquor from the lithium carbonate precipitation step.This utilizes the carbonate present in the lithium carbonatecrystallizer mother liquor and recovers most of the lithium that remainssoluble in the mother liquor.

When recycling mother liquor, it is important to carefully control theCO₃/Mg ratio to prevent lithium carbonate from precipitating with themagnesium carbonate. This is because the lithium concentration at thispoint in the process may be high (0.5 to 1.2 wt % Li), but this becomesless problematic at lower lithium concentrations, e.g., at about 1.0%.After the magnesium carbonate is precipitated and filtered, themagnesium carbonate solids are given a displacement wash using lithiumcarbonate mother liquor to recover some of the concentrated brineretained with the magnesium carbonate solids. Using mother liquor as thewash instead of water reduces the water input to the process that mustbe subsequently removed as a process bleed stream. The mother liquorconstitutes the process bleed whereby all the water (from brine and washwater) and sodium chloride are continuously removed from the process(from soda ash reaction with lithium and magnesium chloride) and whichcontains about 5% of the total lithium in the concentrated feed brine.The washed muds contain between 5 and 12% of the total lithium input andconstitutes a major lithium loss for the process in addition to thelithium lost with the proceed bleed.

The magnesium remaining in the brine (generally from 0.06 to 0.02 wt %Mg) is finally removed by treating the brine with a lime/soda ash(CaO/Na₂CO₃) slurry to form insoluble magnesium hydroxide (Mg(OH)₂) andinsoluble calcium carbonate (CaCO₃). The coprecipitated CaCO₃ acts as afilter aid in filtering the Mg(OH)₂ muds. Additional filter aid may beadded to further improve filtration. The lime/soda ash ratio is adjustedto control the level of soluble calcium remaining in the purified brine.

Because magnesium hydroxide usually precipitates as a gel, it ispreferred to maintain the pH between 8.45 and 9.10 (measured directlywith a slurry pH electrode) in order to achieve maximum filtrationrates. After separation of the solids from the purified brine, the brinecontains between 0.5% Li and 1.2% Li, less than 0.0001 wt % magnesium,less than 0.0015 wt % calcium, and less than 0.0005 wt % boron.

The magnesium-calcium-boron free brine is subsequently treated with asoda ash solution to precipitate lithium carbonate and the mother liquoris recycled as described above. The sodium added to the process asNa₂CO₃ is removed with the mother liquor bleed stream as dissolvedsodium chloride (NaCl). Hot de-ionized water is used to wash the lithiumcarbonate mother liquor from the filtered lithium carbonate crystal toremove sodium and chloride. The lithium in the wash filtrate isrecovered by using the wash filtrate to produce the soda ash solution.

The lithium carbonate product produced by the foregoing process ischaracterized as technical grade, and a typical technical grade lithiumcarbonate contains about 0.04 wt % sodium.

This product is a suitable source of lithium for producing chemicalgrade lithium carbonate having less then 0.04% Na, and subsequently, lowsodium lithium chloride, without need for preparation of lithiumhydroxide and the recrystallization steps of prior art processes.However, the chemical grade lithium carbonate first needs to beprocessed to reduce these impurities to a level suitable for producing alow sodium battery grade lithium chloride. The sodium content in lowsodium lithium carbonate is reduced to below about 0.0002 wt % Na.

Purification of the lithium carbonate to produce low sodium lithiumcarbonate may be conducted in a continuous reactor/crystallizerapparatus as shown in FIG. 4. The apparatus is designed to continuouslydissolve lithium carbonate as lithium bicarbonate (LiHCO₃) by reacting aslurry (3–5% solids) of the technical grade lithium carbonate preparedas described above and water with CO₂ gas at room temperature (minus 10to 40° C.) in a dissolver shown as 3 in FIG. 2. The resultant LiHCO₃solution (7.0–8.5 wt % LiHCO₃) is transferred on a continuous basis to acrystallizer shown as 5 in FIG. 2 which is maintained at 70° C.–95° C.to precipitate high purity lithium carbonate crystals and evolve carbondioxide gas, which may be recycled into the process. Lower temperaturesmay be used in the dissolver shown as 3 in FIG. 2 to increase thelithium bicarbonate concentration per cycle for purification, thereby,increasing equipment throughput.

In the crystallizer shown as 5 in FIG. 2, high purity lithium carbonatecrystals precipitate from the lithium bicarbonate solution at the highertemperature and CO₂ gas is evolved. The slurry is continuously removedand the lithium carbonate crystals are filtered hot and washed withsodium free de-ionized water. The lithium carbonate mother liquorcontains valuable soluble lithium and is recycled to the dissolver shownas 3 in FIG. 2 to minimize lithium loss. The source of CO₂ may be fromthe gas evolved in the crystallizer, from CO₂ generated when reactinglithium carbonate with hydrochloric acid, or from a commercial CO₂source. Use of a commercial CO₂ source yields a simplified process, anddoes not require special added equipment to recover the CO₂.Furthermore, no chemical reagents are required except for sodium freedeionized water. The temperature differential between the dissolvershown as 3 in FIG. 2 and the crystallizer shown as 5 in FIG. 2 definesthe throughput.

The apparatus in FIG. 4 is now described in more detail. Thedissolver/settler is preferably a cooled baffled reactor with a highheight to diameter aspect ratio containing a gas disperse/mixer designedto completely absorb CO₂ gas. The reactor preferably has a minimumactive height of 8 feet. A settler/decanter is incorporated to eliminateundissolved solids from contaminating the clear LiHCO₃ solution beingcontinuously removed from the dissolver. A baffle is preferably placedbelow the decanter to prevent carbon dioxide gas from entering andincapacitating the settler/decanter. The cool LiHCO₃ solution is polishfiltered to remove insoluble impurities, then preheated with therecycled mother liquor in a heat exchanger. A cartridge filter may beincorporated prior to the heat exchanger to remove insolubles. Thepreheated LiHCO₃ solution is then pumped via a pump to a heatedcrystallizer where it is decomposed at between 70 and 95° C. to form lowsodium lithium carbonate crystals, CO₂ gas, and mother liquor. Themother liquor contains dissolved lithium carbonate and a small amount ofLiHCO₃. The mother liquor and CO₂ are recycled back to thedissolver/settler reactor. Sodium is removed from the process using amother liquor process bleed so that the mother liquor contains less than500 ppm sodium. The lithium contained in the mother liquor bleed streamis recovered by using the bleed stream as part of the wash water used onthe filtration equipment for producing technical grade lithiumcarbonate. The number of times the mother liquor is recycled is definedby the sodium content and the degree of purification needed.

As an alternative to using a dissolver/settler for the conversion ofchemical grade lithium carbonate to a LiHCO₃ solution is to employ, forexample, a carbon dioxide absorption column such as shown in FIG. 5, asieve tray column as shown in FIG. 6 or a Scheibel column commerciallyavailable from Glitch Technology Corporation) such as shown in FIG. 7.

Ultra high purity lithium can be produced by passing the LiHCO₃ solutionthrough an ion exchange column prior to decomposing and recrystallizingthe Li₂CO₃, to reduce total impurity content, preferably to less than 10ppm. Of course, the brine may be passed through at any point during theprocess after the magnesium and calcium precipitation steps to removeother impurities. In a preferred embodiment, Amberlite IRC-718 resincommercially available from Rohm and Haas is used in the column. Priorto use, it is preferred to remove sodium from the Amberlite resin, e.g.by passing HCl through the column. A lithium hydroxide solution is thenrun through the column to convert the resin to the lithium form. Thelithium bicarbonate solution (7.5–8% LiHCO₃) is then passed through thecolumn, and the purified solution is heated to 95° C. to precipitate thelithium carbonate which is washed with 95° C. deionized water. The solidis then dried to yield high purity lithium carbonate.

Table 3 shows the typical content of the lithium carbonates prepared bythe processes of the invention:

TABLE 3 CHEMICAL COMPOSITION OF CHEMICAL, LOW SODIUM, AND HIGH PURITYLOW SODIUM LITHIUM CARBONATE Chemical Grade Low Sodium High Purity %Li₂CO₃ 99.38 ± 0.026 99.4 99.995 % Mg  0.004 ± 0.0006 0.0005 ± 0.00020.00001 % Na 0.069 ± 0.005 0.0002 ± 0.001* 0.0002 % K  0.0003 ± 0.000020.00015 ± 0.0001  0.00015 % Ca 0.014 ± 0.001  0.012 ± 0.0014 0.00007 %SO₄ 0.037 ± 0.003  0.003 to 0.037* 0.003 % B  0.0003 ± 0.00001 <0.0001<0.0001 % Cl  0.01 ± 0.006 <0.005 <0.005 % Al 0.0007 0.0002 % As 0.00020.0001 % Fe 0.0005 0.0001 % Si 0.0076 0.001 0.00011 % Zn 0.0001 0.000050.000014 *function of ion concentration in mother liquor recycle

High purity lithium chloride can then be produced from the low sodiumlithium carbonate by conventional reaction in solution with hydrochloricacid such as used in the prior art, except that the hydrochloric acidmust have a low sodium content, e.g. 0.02 wt % sodium or less such thatadditional sodium is not entered into the system as a contaminant.

The lithium carbonate processes are described in more detail withrespect to FIGS. 1 and 2.

Lithium Carbonate Process Flow Diagram A

FIG. 1 shows that (1) solid soda ash is mixed with wash water filtrate(17) to make soda ash solution, SAS (2). In the first stage reactorraffinate 3 containing 6% lithium is mixed with SAS (2), mud from thedirect chloride process (4) and mother liquor (5). This recovers thelithium entrained in the direct chloride muds, removes the magnesium anddilutes the lithium concentration to around 1%.

(7) The MgCO₃ mud (8) is separated from the brine and washed with motherliquor. The wash filtrate and the filtered brine are combined and sentto the second stage reactor (12).

(12) In the second stage reactor, reagent (11) which is a combination oflime (9) and SAS (2) is added to precipitate Mg(OH)₂ and CaCO₃ (14)which are removed by filtration (13).

(15) In the lithium carbonate reactor SAS (2) is added to precipitatelithium carbonate. The solid is separated from the mother liquor byfiltration (18). The mother liquor is recycled and excess is removedthrough (19). The lithium carbonate is washed with water (16) which isrecycled through (17) and used in the production of SAS (2)

(20) A portion of the wet lithium carbonate from the filter is sent to(B1) to be used in the production of low sodium lithium carbonate andthe majority is sent to the dryer (21) and packaged as technical lithiumcarbonate (22).

FIG. 2

Low Sodium Lithium Carbonate Process Flow Diagram B

(1) Wet lithium carbonate from (A20) is used as feed material.

(2) Lithium carbonate is mixed with the bicarbonate/carbonate motherliquor recycle and fed into the lithium bicarbonate sparger reactor (3).

(3) Carbon dioxide gas is bubbled into the reactor where it reacts withthe lithium carbonate forming lithium bicarbonate.Reaction#1: H₂O+CO₂+LiCO₃ - - - >2LiHCO₃

(4) Lithium bicarbonate solution is filtered to remove insoluble andun-reacted small particles that are not removed by the settler.

(5) Lithium bicarbonate solution is heated to 90″ C to reverse Reaction#1 and precipitate purified lithium carbonate.Reaction #2:2LiHCO₃ - - - >LiCO₃+CO₂+H₂O

(6) Lithium carbonate is separated from mother liquor and washed with90° C deionized water from (7) on filter (6).

(8) Lithium carbonate is packaged in maxi sacks and stored untilprocessing in the direct lithium chloride plant at (C18) or dried toprovide low sodium lithium carbonate.

(9) Mother liquor from the bicarbonate/carbonate crystallizer and washwater are recycled and a bleed (10) equal to the input wash is removedand used in the lithium carbonate plant product as wash water (A16).

(11) Carbon dioxide gas used in the generation of lithium bicarbonatesolution is recycled from the bicarbonate/carbonate crystallizer and amake up source (12) is used to compensate for system leaks and to keep aconstant pressure to the lithium bicarbonate sparger reactor (3)

(13) A heat exchanger is used to preheat the bicarbonate solution priorto the precipitation tank and conserve system heat.

To increase the rate of conversion of lithium carbonate to lithiumbicarbonate, it is preferred to employ baffles and dual pusherpropellers to maximize the time that a bubble of carbon dioxide remainsin solution. Increasing the height of the vessel also increases theresidence time of the carbon dioxide. It was also discovered that usinglithium carbonate with an average particle size of from about 75 toabout 425 microns, and preferably less than 250 microns, most preferablyabout 425 microns, also increases conversion rates of lithium carbonateto lithium bicarbonate.

It was also discovered that technical grade lithium chloride can bedirectly precipitated from the same starting brine (about 6.0 wt % Li)used to prepare the low sodium lithium carbonate as described above.Thus, the process of the present invention produces a technical grade oflithium chloride product that is made directly from concentrated naturalbrine containing essentially 6 wt % lithium from which boron has beenremoved by the described extraction process of Brown and Boryta (U.S.Pat. No. 5,219,550). The lithium chloride produced by this process isessentially higher in purity with respect to sodium and calcium content.Using quick lime (CaO) instead of slaked lime (Ca(OH)₂) to precipitatemagnesium as a double salt gives better filtration properties andimproved lithium yield as concentrated brine than what can be achievedusing the Chilean Patent application 550–95. Brine concentrated to lowerlithium concentrations may also be treated by this method. However, themagnesium to lithium ratio is minimized when the concentration oflithium can be increased to approach the endpoint concentration of thesystem, i.e., 6 wt % Li, 1.7 wt % Mg, thereby minimizing the amount ofmagnesium that has to be removed.

The process involves removing the magnesium from the brine as a doublesalt using excess quick lime (CaO), separating the magnesium and calciummuds by filtration, cooling the filtered brine to reduce the sodium byprecipitating sodium chloride, separating the sodium chloride solids byfiltration, diluting the filtered brine slightly (to 29% LiCl) andtreating the filtered brine with oxalate (oxalic acid) and barium(barium chloride) to remove precipitated calcium oxalate and bariumsulfate, and subsequently crystallizing lithium chloride directly fromthe purified brine, e.g. in a vacuum crystallizer. The process mayutilize the mother liquor produced in the process for preparing lithiumcarbonate as shown in FIG. 1 to recover the lithium lost to themagnesium removal step as described above. The use of lithium carbonatemother liquor improves the overall recovery of lithium as commercialproducts.

The process eliminates the need for using hydrochloric acid to producelithium chloride from lithium carbonate and/or the LiOH·H₂O as in theprocesses of the prior art. The resultant chemical grade lithiumchloride process of the invention application has essentially 5 majorsteps described as follows:

1) Preparation of a low boron aqueous solution from natural brine andconcentrating to a lithium content of about 6 wt %;

2) Removing magnesium and calcium by precipitation and filtration.

3) Cooling the brine to reduce the sodium content;

4) Adding oxalate and barium to remove calcium and sulfate; and

5) Direct crystallization of lithium chloride.

The 6 wt % lithium brine is prepared as described above, e.g. by solarevaporation. The purification of the boron free concentrated brinecontaining essentially 6 wt % lithium is described in more detail asfollows:

Magnesium is removed from the brine by adding enough quick lime to formmagnesium and a calcium insoluble double salts. The use of quick limeinstead of slaked lime improves the filterability of themagnesium/calcium containing muds and improves the overall brine yieldcontaining lithium. according to the follow reaction which occurs inlithium concentrated brine at Ca(OH)₂/Mg mole ratio from 2–3:

The filtration properties and lithium yield as brine improvessubstantially using quick lime (CaO) compared to slaked lime (Ca(OH)₂).In order to maintain the calcium insoluble, the Ca to Mg mole ratio forquick lime addition is preferably between 3 and 4 and the reaction isset forth below:

Regardless of whether quick lime or slaked lime is used, the process istypically conducted at temperatures ranging from about 25° C. to about120° C. If filtration becomes a production rate controlling variable,then the temperature may be increased to precipitate both magnesium andcalcium.

The final pH of the brine after completion of the reaction generallyranges from about 9.5 to about 12.0 measured at 1:10 dilution withwater.

Excess slaked lime or additional reaction time may be used as a processcontrol.

In a preferred embodiment, lithium lost to the lithium chloridemagnesium purification solids may be recovered by re-slurrying thesemuds in the reactor for precipitating magnesium carbonate in the lithiumcarbonate process.

Compared to the magnesium removal steps described above for preparationof lithium carbonate (FIG. 1 (6)), an overall increase in lithium yieldmay be obtained for this purification step by adding magnesium andcalcium double salt purification muds (FIG. 1 (4)) from the directlithium chloride process.

Sodium may be removed to acceptable levels by either cooling before orafter magnesium removal. However, cooling before magnesium removal alsosalts out LiCl·H₂O because the brine is saturated with respect tolithium chloride and magnesium chloride. To overcome the loss oflithium, an extra filtration step may be used to recover the lithiumprecipitated followed by recycling the LiCl·H₂O salt.

In a preferred embodiment, magnesium is removed first by addition oflime followed by cooling the brine containing 6% Li to from minus 30 to+10° C., preferably below 0° C., and more preferably −15° C. to −20° C.,preferably from −30 to below −20° C., to reduce sodium concentration toless than 0.05 wt % sodium in the brine. This level of sodium is lowenough for producing a chemical grade of lithium chloride crystal thatcan be used as feed salt to produce lithium metal containing less than1% Na. Removal of magnesium prior to cooling in essence produces adilute brine with respect to lithium chloride, thereby substantiallyeliminating a lithium loss at this point in the process. A substantialportion of the calcium concentration in the brine when magnesium isremoved is initially controlled by the quick lime addition in excess ofa Ca/Mg mole ratio of 3, or by adjusting the pH above 11 by adding quicklime.

Removing the remaining calcium as insoluble calcium oxalate and sulfateas barium sulfate by the addition of oxalic acid and barium chloride,respectively, may be done in the same reactor with a single filtrationstep. Lithium oxalate and barium chloride are preferred salts for theprecipitation step, although others may be used. Removal of calcium andsulfate may be done either before or after the sodium removal step. Thebrine is preferably diluted to between 29 and 33 wt % lithium chloridefor this step. Therefore, it is preferred to conduct this purificationstep after the sodium removal.

In preferred embodiments, the calcium/sulfate removal is conducted byfirst lowering pH to about 10.0 by addition of concentrated HCl, andthen adjusting the calcium concentration to 500 ppm by the addition ofcalcium chloride. The pH of the brine is then adjusted to a pH ofbetween 7.0 and 4.0.

In a particularly preferred embodiment, a solution of lithium oxalate isadded to the brine at a ratio of 1.5 moles lithium oxalate to 1.0 molecalcium. Barium chloride is added at a 1:1 molar ratio to precipitatethe sulfate. The brine is mixed and allowed to react for between 4 to 24hours. Preferably, the lithium oxalate is added first, the reactionallowed to continue for about 4 hours. Then the pH is adjusted to about7.0, and the barium chloride is then added to precipitate the sulfate asbarium sulfate. The filtered lithium chloride solution will then beready for the crystallizer.

The final brine is evaporated to dryness to recover the lithiumchloride. Alternatively, the brine can be used as a crystallizer feedbrine to precipitate anhydrous lithium chloride.

To produce anhydrous lithium chloride from solution, it is preferred toconduct the crystallization in an evaporation crystallizer operating ata temperature above 110° C. If impurities reach unacceptableconcentrations, the crystallizer solution may be returned to thepurification steps for adjustment.

An example of the lithium chloride purity produced by the above processis as follows:

LiCl 99.0 wt % Na 0.09–0.11 wt % Ca 0.0015–0.003 wt % Mg <0.0003 wt % Ba0.007 wt % SO₄ 0.007 wt % Si 0.004 wt %

The direct lithium chloride process is now described in more detailbelow with respect to FIG. 3. (1) CaO and low boron raffinate feedcontaining 6% lithium (2) are fed into the liming tank (3) where theyare mixed at a weight ratio of 15 % lime to brine, they are mixed untila pH greater than 11.0 as measured on a filtered sample diluted 1:10with water.

(4) The slurry produced in the liming tank is filtered to separate themagnesium free brine from the Ca/Mg mud. The brine is sent to thefiltrate tank (6) and the mud is sent to the muds tank (5) where it canbe slurried and pumped to the lithium carbonate plant (A4 in FIG. 1) forrecovering the entrained lithium in the first stage of the lithiumcarbonate plant (shown in FIG. 1 as 6).

(7) The magnesium free brine is fed into the cooling reactor toprecipitate sodium chloride to acceptable levels and is filtered attemperature in (8). The solids (9) are sent to waste or for lithiumrecovery in the carbonate plant. The low sodium brine is sent to thepurification tank (10).

(10) In the purification tank water is added to dilute the magnesiumfree low sodium brine to 33% lithium chloride, HCl is added to adjustthe pH to 4.0 and barium chloride is added to precipitate barium sulfatefrom the brine. The pH is raised to 10.0 with lithium hydroxidemonohydrate and lithium oxalate is added to precipitate calcium oxalate.

(12) The solution is filtered to remove the barium sulfate, calciumoxalate, and magnesium hydroxide solids and is sent to the adjustmenttank (13) for a final pH adjustment to 7.0 for feed to the crystallizer(14) and dryer (15) to produce anhydrous technical lithium chloride (17)

(16) An optional pure lithium chloride wash solution can be employed toreduce potassium levels for technical lithium chloride

(18) Low sodium lithium carbonate from (FIG. 2 B8) is reacted withhydrochloric acid to produce a high purity lithium chloride solution,which is fed into the purification tank (10) and treated for sulfate andcalcium as before to produce battery grade anhydrous lithium chloride.

The invention also relates to a method for purifying metal carbonatesthat are insoluble in water but have corresponding metal bicarbonatesalts that are more 75% by wt. soluble in water by prepare an aqueousslurry of said metal carbonate; introducing carbon dioxide gas into saidaqueous slurry to form a corresponding metal bicarbonate solution; andheating the metal bicarbonate solution to form a purified metalcarbonate, wherein the heating is such that the temperature of thesolution is raised to a temperature at which the metal carbonate isinsoluble to precipitate the purified metal carbonate. Lithium is apreferred metal, but any metal having a carbonate that is insoluble inwater, preferably at a temperature of 70–95° C., but wherein thebicarbonate is at least 75% soluble (by weight), may be used inaccordance with the present invention. Thus, a general method ofproviding purified metal carbonates is also a part of the invention.

EXAMPLE 1 Preparing Low Sodium Lithium Carbonate

To a concentrated brine containing 6.19% Li, 1.51% Mg, 0.179% Na, 0.026%K, 0.056% Ca, 0.002% SO₄, 0.0003% B, and 36% Cl, recycled mother liquorcontaining 0.14% Li, 8.26% Na, 0.18% SO₄, 12.37% Cl, and 0.58% CO₃ wasadded at a temperature of 70° C. Enough mother liquor was added to forma solution containing 1% Li. This also precipitated most of themagnesium as magnesium carbonate and basic magnesium carbonate. Thesolution was filtered to remove the precipitated magnesium. Themagnesium remaining in solution was removed by adding a limed soda ashreagent which also reduced calcium as an insoluble calcium carbonatesolid. The resultant purified brine was filtered and contained 1% Li,0.0002% Mg, 0.0024% Ca, 6.9% Na, 15.5% Cl. A soda ash solution wasprepared using lithium carbonate wash water filtrate and added to thepurified brine. The lithium carbonate crystals were filtered andsubsequently washed with hot de-ionized or distilled water andsubsequently used as the feed to the bicarbonate reactor. The lithiumcarbonate filtrate, which is the mother liquor, was recycled to theprocess, and the wash filtrate was recycled to prepare the soda ashsolution. A portion of the mother liquor was discharged from the processto remove the excess water and sodium chloride accumulated in theaqueous phase.

The filtered lithium carbonate crystals, a cooled mixture of recycledlow sodium lithium carbonate mother liquor filtrate and wash waterfiltrate, and carbon dioxide gas from the low sodium lithium carbonatecrystallizer were fed continuously to form a slurry in a baffledbicarbonate reactor. The carbon dioxide gas was dispersed using ahigh-speed mixer. The carbon dioxide gas and the mother liquor/washfiltrate solution were fed to the bottom of the reactor. This formed abicarbonate solution that was filtered and sent to the lithium carbonatecrystallizer. In this example the reactor temperature to form thebicarbonate solution was controlled between 0° C. and 35° C. The lithiumcarbonate feed rate was controlled to maintain as much suspended solidsas possible. The liquid volume of the entire system was maintainedconstant and the excess liquid volume generated by the addition of thewash filtrate was used as the process bleed.

Prior to feeding the cool bicarbonate solution to the crystallizer, itwas filtered to remove insoluble impurities and heated in a heatexchanger to recover the heat contained in the recycled mother liquorand wash filtrate. The preheated bicarbonate solution was thencontinuously added to the heated bicarbonate decomposer/lithiumcarbonate crystallizer maintained at 70° C. to 90° C. The lithiumcarbonate solids and the liquid were continuously removed and filteredhot. The filtered low sodium lithium carbonate crystals werecontinuously washed with hot distilled water then dried. The motherliquor and the wash filtrate were recycled to the bicarbonate reactorvia a heat exchanger.

Table 4 gives an example of the production rate for the continuouspurification apparatus described according to the conditions inExample 1. Table 5 gives the analysis of products produced.

TABLE 4 RELATION OF PRODUCTION RATE AND TEMPERATURE IN AN APPARATUS FORCONTINUOUSLY PRODUCING LOW SODIUM LITHIUM CARBONATE REACTOR TEMPERATURE,° C. Li2CO3 CRYSTALLIZATION RATE, LiHCO₃ Li₂CO₃ grams/hour 35 70 45.4 3590 89.2 10 70 108.9  0 70 113.4 10 90 133.5  0 90 195.2

TABLE 5 CHEMICAL ANALYSIS (DRY BASIS) Low Sodium Li2CO3, ppm Li2CO3Feed, ppm (average from Example 1) Na 800 4.0 ± 0.7 Mg 28 6.3 ± 1   Ca81 34 ± 14 S 120 16 ± 16 B 1.2  0.5 ± 0.04 Si 82 4.5 ± 1.5 Fe 3.3 1.2 ±0.3

EXAMPLE 2 Preparing Ultra High Purity Lithium Carbonate

Ultra high purity lithium carbonate was prepared as described above inthe same equipment to which was added an ion exchanger between thefilter and the heat exchanger. The ion exchange column contains Rohm andHaas, Amberlite IRC-718. The purity of this product is listed in Table6.

TABLE 6 ULTRA HIGH PURITY LITHIUM CARBONATE (EXAMPLE 2) Wt %Li2CO3 >99.995 Mg <0.00001 Na <0.0004 K <0.00015 Ca <0.00007 SO4 <0.003B <0.0001 Cl <0.005 Si <0.0001 Zn <0.00001 Cr <0.00001 Cu <0.0001 Fe<0.0001 Ni <0.0001 P <0.006

EXAMPLE 3 Preparing Low Sodium Lithium Chloride

Hydrochloric acid (35% conc.) containing less than 0.00015% sodium wasreacted with lithium carbonate prepared in Example 1. The resultingsolution was evaporated to crystallize lithium chloride. The lithiumchloride was filtered from the evaporated solution and dried.

EXAMPLE 4 Preparing Ultra High Purity Lithium Chloride

As in Example 2, ultra-high purity lithium chloride was prepared bypassing the lithium chloride solution described in Example 3 through anion-exchange column to further reduce divalent and trivalent impurities.The solution was crystallized to make ultra-high purity lithiumchloride.

EXAMPLE 5 Low Sodium Lithium Carbonate Using an Absorption Column

The diagram in FIG. 5 was the laboratory set-up used from which thelarger scale tests were done using a sieve tray column (FIG. 6) andScheibel column (FIG. 7).

The method followed that already described in Example 1. The purifiedproduct had the same composition as in Example 1. This demonstrated thatabsorption of carbon dioxide can be accomplished in a typical reactorwith a bubbler or an absorption column.

Other facets of the invention will be clear to the skilled artisan, andneed not be set out here. The terms and expression which have beenemployed are used as terms of description and not of limitation, andthere is no intention in the use of such terms and expression ofexcluding any equivalents of the features shown and described orportions thereof, it being recognized that various modifications arepossible within the scope of the invention.

1. A continuous process for directly preparing high purity lithiumcarbonate from lithium containing brines comprising: preparing a brinecontaining about 6.0 wt % lithium and further containing other ionsnaturally occurring in brines; adding mother liquor containing carbonatefrom a prior precipitation step to precipitate magnesium as magnesiumcarbonate; adding a solution of CaO and sodium carbonate to removecalcium and residual magnesium; precipitating lithium carbonate from thepurified brine by adding soda ash solution; filtering the resultantsolution to obtain solid lithium carbonate; preparing an aqueous slurryof the lithium carbonate in a reactor equipped with an inlet forintroducing carbon dioxide gas and introducing carbon dioxide gasthrough the inlet into said aqueous slurry to form an aqueous lithiumbicarbonate solution, the reactor being at a temperature from at leastminus 10 to 40° C.; passing said aqueous lithium bicarbonate solutionthrough a filter to clarify the solution and optionally an ion exchangecolumn for further calcium and magnesium removal; introducing saidfiltered lithium bicarbonate solution into a second reactor andadjusting the temperature of the solution to from 60–100° C. toprecipitate ultra-pure lithium carbonate with sodium less than 0.0002 wt%, calcium less than 0.00007 wt % and magnesium less than 0.00001 wt %.2. The process of claim 1 wherein the lithium bicarbonate is only passedthrough a filter and proceeding to the second reactor at 60–100° C. toprecipitate low sodium lithium carbonate with a sodium content of lessthan 0.0002 wt %.
 3. The method of claim 1, wherein the temperature inthe reactor is from 0–35° C., and the temperature of the reactor forprecipitating high purity lithium carbonate is from 70–95° C.
 4. Acontinuous process for directly preparing high purity lithium carbonatefrom lithium containing brines comprising: preparing a brine containingabout 6.0 wt % lithium and further containing other ions naturallyoccurring in brines; adding CaO to remove magnesium; adding motherliquor containing carbonate from a prior precipitation step and soda ashsolution to precipitate calcium carbonate; filtering to remove calciumcarbonate and to yield a purified lithium containing brine; adding sodaash to said purified brine to precipitate lithium carbonate; filteringthe solution to recover the precipitated lithium carbonate, preparing anaqueous lithium carbonate slurry in a reactor where such reactor isequipped with an inlet for introducing carbon dioxide gas andintroducing carbon dioxide gas through the inlet into the lithiumcarbonate slurry to produce an aqueous lithium bicarbonate solution,wherein the reactor is at a temperature from at least minus 10 to +40°C.; passing the aqueous lithium bicarbonate solution through aclarifying filter and optionally an ion exchange column for furthercalcium and magnesium removal; introducing the filtered solution into asecond reactor and adjusting the temperature of the solution to from60–100° C. to precipitate the ultra-pure lithium carbonate with sodiumless than 0.0002 wt %, calcium less than 0.00007 wt % and magnesium lessthan 0.00001 wt %.
 5. The process of claim 4 wherein the lithiumbicarbonate is only passed through a filter and proceeding to the secondreactor at 60–100° C. to precipitate low sodium lithium carbonate with asodium content of less than 0.0002 wt %.
 6. The method of claim 4,wherein the temperature in the reactor is 0–35° C., and the temperatureof the reactor for precipitating high purity lithium carbonate is from70–95° C.
 7. The method of claim 4, wherein the method is conducted atless than or equal to atmospheric pressure.
 8. High purity lithiumcarbonate, comprising less than 20 ppm sodium as an impurity.
 9. Highpurity lithium carbonate, comprising less than 2 ppm sodium as animpurity.
 10. Purified lithium carbonate comprising: greater than 99.4wt. % Li₂CO₃; less than 0.0007 wt. % Mg; less than 0.0010 wt. % Na; lessthan 0.00025 wt. % K; less than 0.0120 wt. % Ca; less than 0.0001 wt. %B; less than 0.0002 wt. % Al; less than 0.0001 wt. % As; less than0.0001 wt. % Fe; less than 0.0010 wt. % Si; less than 0.00005 wt. % Zn;less than 0.037 wt. % SO₄; and less than 0.005 wt. % Cl.
 11. Purifiedlithium carbonate comprising: greater than 99.995 wt. % Li₂CO₃; lessthan 0.00001 wt. % Mg; less than 0.0002 wt. % Na; less than 0.00015 wt.% K; less than 0.00007 wt. % Ca; less than 0.0001 wt. % B; less than0.0002 wt. % Al; less than 0.0001 wt. % As; less than 0.0001 wt. % Fe;less than 0.00011 wt. % Si; less than 0.000014 wt. % Zn; less than0.0030 wt. % SO₄; and less than 0.005 wt. % Cl.